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SX-1280 Main Cap Replacement

EchoWars

EchoWars

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Here's a pic of the finished deal...I had meant to snap a pic of the 'before', but sometimes I jump into the work and forget that some documentation would be nice.

newcapscloseup22zh.jpg


The stock caps are 15,000µf 100V caps with wire-wrap terminals, and a bizarre ground bus that connects the common terminals. Of course, the stock metal bus piece is useless with the new 22,000µf 100V Nippon Chemi-Con screw terminal caps, so I used a piece of 10ga solid wire bent around a 52mm cap that was laying around for a nice pretty bend, and then used a piece of 14ga solid to wrap around the center of the bend a couple of loops (try it with 14ga wire, not as easy as you might think), and soldered it in place after adding a loop terminal to the end.

All the terminations are soldered, and the end result is (to me at least) as pretty as it is functional.

Just wish I had taken a 'before' pic... :sigh:
 
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VintageNut said:
Would I need a high wattage soldering gun to solder that heavy wire?
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I was going to ask about that connection too. Did you do that with flame, or an iron? Looks super. :yes:
 
the bypass caps are 2.2uf polypropylenes by the looks of it. The exact value chosen is not critical. I presume he put it there to filter out some of the random electrical noise (alternating current). Also because of the wires which may act like antennas and pick up electrical noise. This noise is also referred to as "ripple". The ripple shows up as a fluction of voltage (in the range of 5-10 milivolts).

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In "macro-electronics" (OK, I'm an electrician) we have small resistors across all capacitors in high intensity lighting and motor starting capacitors. The purpose in these cases is for safety reasons. It allows the caps to immediately discharged once the power is off. In my trade, they're called "service resistors".
 
kcollins4 said:
In "macro-electronics" (OK, I'm an electrician) we have small resistors across all capacitors in high intensity lighting and motor starting capacitors. The purpose in these cases is for safety reasons. It allows the caps to immediately discharged once the power is off. In my trade, they're called "service resistors".
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I find that to be shocking!
 
If you examine an electrolytic cap's construction, you will note that it is a enormous foil coil. A coil is also an inductor. Coils have rising impedance with frequency, which is a bad thing in power supply caps. The small bypass cap parallels the big cap, but it has significantly less inductance, so high frequencies see the lower impedance of the small cap. Thus they are filtered, or "bypassed".
BTW, this cap is a .22 mF poly, not 2.2.
 
2200000pf (five zeros) = 2,200nf = 2.2µf

It's just the standard value I have laying around for this purpose. These are actually fairly cheap metal polyester caps, but that's all that is needed to do the job here.

The 1280 has bleed resistors, but they are mounted on the diode board rather than directly on the caps.
 
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I know it's an old thread but what is the significance of raising the capacitance from 15K to 22K? My assumption is that it will allow for higher peak power levels but not continuous? I also assume it has nothing to do with actual sound characteristic, just power supply. Will it actually raise the peak output by roughly 30% since the value is about 30% higher?
 
It is to utilize the same physical mounts, increasing the capacitance and voltage to get a cap the same diameter as the original. The surge limiter that controls the inrush current initially compensates for the greater inrush current of the larger capacitance.

In the units without toroidal transformers, the e-i cores saturation does the limiting. Then we have to watch out for the rectifiers feeding the caps - can THEY handle the increased capacitance?

Jury rigging alternate mounts for smaller diameter main caps is one of the major pita's of installing new main caps.
 
biggal76 said:
I know it's an old thread but what is the significance of raising the capacitance from 15K to 22K? My assumption is that it will allow for higher peak power levels but not continuous? I also assume it has nothing to do with actual sound characteristic, just power supply. Will it actually raise the peak output by roughly 30% since the value is about 30% higher?
Click to expand...
I usually buy 63mm 22,000uf 100V screw-terminal caps in job lots (20 or more), since so many units can use them. SX-1250, Spec 2, Spec 4, SX-1280, SX-1050, SX-1080, etc, etc, etc... Prices fluctuate a lot, so when I see that Digikey or Mouser or whoever has a good price on some reliable brand I'll grab a bunch of 'em. Saves me from having to stock a bunch of different sizes.

The power output is dependent on the available voltage, and that is determined by the transformer. The extra capacitance will 'stiffen' the supply rails a bit at full power, but actual power gains might end up being a couple of watts at best.
 
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